This invention relates to an apparatus for detecting and processing a radiation image capable of obtaining a radiation image suitable for diagnosis and so forth.
Heretofore, as a method for obtaining an image signal of a radiation image such as an X-ray image of a human body for diagnosing a disease, a method of reading a photographic film image and a method of using a stimulable phosphor have been known.
In this method reading a photographic film, a laser beam is applied to a radiation photographic film having been subjected to processes such as chemical development and fixing, and the transmitted or reflected light from it is converted into an electrical signal by means of a photoelectric element such as a photo-multiplier tube to obtain image data for each of pixels.
On the other hand, in the method of using a stimulable phosphor, it is utilized a stimulable phosphor, which stores a part of radiation energy, and when a stimulating light such as a visible light is applied, shows stimulated luminescence in accordance with the stored energy, and after radiation image information of a subject is recorded on the stimulable phosphor plate formed of this stimulable phosphor, a laser beam or the like is applied to it so that the stimulated luminescence may be converted to obtain the image data of each pixel.
As mentioned in the above, in the method reading a photographic film or the method using a stimulable phosphor, the radiation image based on the obtained image data becomes an image having a lowered sharpness, because the image data are obtained by collecting the transmitted light, reflected light, or the stimulated light emission. For this reason, image processing is executed for correcting the lowered sharpness.
Further, as a method which can obtain image data without collecting the transmitted light, reflected light, or the stimulated light emission as done in the method reading a photographic film or the method using a stimulable phosphor, it is known a radiation image reading means using an FPD (a Flat Panel Detector), which reads a radiation image with a plurality of detecting elements arranged two-dimensionally. In this method using an FPD, a radiation image having a high sharpness can be obtained, because the image data is generated on the basis of the amount of radiation detected by the respective detecting elements.
However, in the FPD as mentioned above, when the amount of radiation becomes low owing to the variation of exposure conditions etc., S/N ratio is reduced and the image data in proportion to the amount of radiation can not be obtained; hence, it happens a case where a good radiation image suitable for a diagnosis can not be obtained.
Therefore, according to the object of this invention, it is provided an apparatus for detecting and processing a radiation image capable of obtaining a radiation image suitable for a diagnosis by correcting the influence owing to the variation of the exposure conditions and so forth.
The above object can be attained by the following structure.
(1) An apparatus for processing a radiation image, comprises:
detecting means having a plurality of detecting elements which are arranged in two dimensional arrangement, for radiographing the radiation image by the plurality of detecting elements, for converting the radiographed radiation image into electric signals as image signals, and for outputting the image signals; and
image processing means for applying image processing to the image signals, the image processing means comprising normalization processing means for converting the image signals into normalized image signals which are proportional to an amount of radiation irradiated to the detecting means or to a logarithm of the amount of the radiation and includes a predetermined signal value.
Further, the above object can be attained by the following preferable structure.
(2) An apparatus for detecting and processing a radiation image of this invention comprises means for detecting a radiation image which radiographs a radiation image by a plurality of detecting elements arranged two-dimensionally and outputs an image signal generated on the basis of the electrical signal obtained by the plurality of detecting elements, and an image processing means which executes image processing to the image signal outputted from said means for detecting a radiation image, wherein said image processing means comprises a normalization processing means which converts the image signal into a normalized image signal being directly proportional to the quantity or the logarithm of the amount of the radiation applied to the means for detecting a radiation image and including a predetermined signal value determined beforehand, and a gradation processing means which executes a process converting at least the gradation for the normalized image signal obtained by the gradation processing means.
Further, the apparatus for detecting and processing a radiation image of this invention comprises means for storing noise characteristics which stores the information on the noise characteristics peculiar to the means for detecting a radiation image, and carries out the process converting the image signal into a normalized image signal by the normalization processing means using said information on the noise characteristics stored in said means for storing noise characteristics.
Further, the apparatus for detecting and processing a radiation image of this invention comprises means for storing the information on radiographing which stores the control information regarding radiographing, and determines the image processing conditions by the aforesaid image processing means using the information on radiographing stored in said means for storing the information on radiographing.
Besides, the aforesaid image processing means comprises means for setting a region of interest which sets the desired region of interest by analyzing the image signal, and means for determining a representative signal value which determines at least one representative signal value on the basis of the image signal in the set region of interest, and carries out conversion into the normalized image signal such that the representative signal value determined by said means for determining a representative signal value corresponds to the aforesaid predetermined signal value.
Further, the image processing means comprises means for storing gradation conversion curves which stores a plurality of gradation conversion curves and means for storing standard gradation conversion curves which stores a plurality of standard gradation conversion curves, and by selecting one out of said plurality of gradation conversion curves stored in said means for storing gradation conversion curves, or by selecting one out of said standard gradation conversion curves stored in said means for storing standard gradation conversion curves to produce the desired gradation conversion curve by deforming the selected standard gradation conversion curve, converts the gradation of the normalized image signal by the gradation processing means on the basis of the selected gradation conversion curve or the produced desired gradation conversion curve.
Furthermore, the image processing means comprises means for enhancing frequency which carries out frequency enhancing processing and means for dynamic range compression-processing which carries out the compression-processing of dynamic range.
In this invention, the image signal is converted into the normalized image signal by carrying out the normalization based on the information on noise characteristics peculiar to the means for detecting a radiation image, for the image signal from the means for detecting a radiation image. Further, using the control information concerning image acquisition (radiographing), by selecting one out of gradation conversion curves, or by selecting one out of standard gradation conversion curves to produce the desired gradation conversion curve by deforming this selected standard gradation conversion curve, gradation processing is executed for the normalized image signal on the basis of the selected gradation conversion curve or the desired gradation conversion curve. Moreover, frequency enhancing processing and dynamic range compression-processing are also carried out.
Further, in normalizing the image signal, the desired region of interest is set from the image signal, and at least one representative signal value is determined on the basis of the image signals in this region of interest; or a signal area corresponding to the portion of a subject is extracted on the basis of the histogram of the image signals in the region of interest, and the approximately minimum value, the approximately maximum value, or a signal value to make the cumulative histogram value in this signal area a predetermined value is made to be the representative signal value; thus, the conversion is done in a manner such that this representative signal value corresponds to the predetermined signal value.
Furthermore, it is preferable to use the abovementioned apparatus (1) or (2) in combination with the following structures (3), (4) and (5) respectively.
(3) An apparatus for detecting an irradiation field comprises means for detecting a radiation image which detects the exposure to a subject with the diaphragm limited by a plurality of detecting elements arranged two-dimensionally, and generates the image data of the radiation image, means for obtaining image data which divides the radiation image into a plurality of blocks and reads out the image data of the respective blocks from said means for detecting a radiation image in a parallel manner, means for storing the position of blocks which stores the positions of the respective blocks on the image, means for detecting a candidate edge point which detects one or a plurality of candidate edge points being considered as positioned on a border of an irradiation field for each of the blocks, on the basis of the image data of the respective blocks read out from said means for detecting a radiation image by said means for obtaining image data, and means for forming the border of an irradiation field which forms it as the border of an irradiation field the figure formed by connecting the candidate edge points detected by said means for detecting a candidate edge point, and detects the area surrounded by the border of an irradiation field as the area of the irradiation field.
(4) An image processing apparatus comprises means for detecting a radiation image which detects the quantity of radiation applied and detects a radiation image by generating an electrical signal corresponding to the detected quantity, means for obtaining image data which divides the radiation image into a plurality of blocks and reads out electrical signals from said means for detecting a radiation image in a parallel manner for the respective blocks to generate image data, and means for forming a reduced image which extracts image data at a predetermined position out of the read out image data to form a reduced image at the time of reading out the image data from said means for obtaining image data.
(5) An image processing apparatus comprises means for detecting a radiation image which detects the exposure and detects a radiation image by generating an electrical signal corresponding to the detected amount, means for obtaining image data which divides the radiation image into a plurality of blocks and reads out electrical signals from said means for detecting a radiation image in a parallel manner for the respective blocks to generate image data, means for calculating a representative value of a block which calculates the representative values of the image data for the respective blocks when reading out the image data from said means for obtaining image data, and means for forming a reduced image which forms a reduced image based on the respective signals for one pixel made of said representative values of the respective blocks obtained by said means for calculating a representative value of a block.